The present invention is directed to data communications using asynchronous transfer mode. More particularly, the present invention is directed to transferring data communications from one asynchronous transfer mode switched virtual circuit to another asynchronous transfer mode switched virtual circuit without interruption of service.
Asynchronous Transfer Mode (xe2x80x9cATMxe2x80x9d) is a switching technology based on switching and multiplexing techniques selected by the International Telecommunication Union (xe2x80x9cITUxe2x80x9d). ATM utilizes a small fixed-size packet, referred to as an ATM cell. Each ATM cell is 53 octets (one octet equals one byte) long and is divided into a header of 5 octets and an information field of 48 octets that is sometimes referred to as a payload.
The ITU has further defined ATM adaptation layers (xe2x80x9cAALsxe2x80x9d). An AAL is the upper layer of the ATM layer and is responsible for converting user information from higher layers into a 48 octet payload field while the ATM cell layer adds the 5 octet header to make the 53 octet ATM cell. A family of AALs, AAL1 through. AAL5, has been defined to handle diverse user applications. The AAL is usually subdivided into two parts: the Common Part Convergence Sub-layer (xe2x80x9cCPCSxe2x80x9d) and the Service-Specific Convergence Sub-layer (xe2x80x9cSSCSxe2x80x9d). The SSCS defines formatting for different applications onto ATM cells.
AAL2 can handle compressed voice through the use of variable size packets, sometimes referred to as xe2x80x9cmini-packets.xe2x80x9d In AAL2, multiple channels are typically multiplexed onto a single ATM switched virtual circuit (xe2x80x9cSVCxe2x80x9d). In a network environment where there are multiple network devices communicating with each other, switching at the AAL2 layer is required. Specifically, an ATM switch must first de-multiplex incoming AAL2 packets over an ATM SVC and then switch the AAL2 packets to the appropriate outgoing ATM SVC. The AAL2 packets are then multiplexed for transmission again.
A regular ATM switch, with minor modifications to its line interface cards, can accomplish this mini-packet switching function. Implementation is straight-forward and relatively simple. However, this adds a layer of complexity to the ATM switch. Further, call signaling at the AAL2 layer is needed, and industry standards for this have not yet been adopted.
Therefore, in some situations, there may be advantages to having a single channel per ATM SVC instead of multiplexing multiple channels onto a single SVC. Having a single channel per ATM SVC is referred to as single channel adaptation (xe2x80x9cSCAxe2x80x9d). SCA avoids the necessity of having to de-multiplex and multiplex at the packet level. As a consequence, standard ATM switching can be used.
SCA can be used over any AAL, including AAL2 and AAL5. When using SCA, a major concern is how to handle facsimile or modem-based telephone calls (referred to as xe2x80x9cfax callsxe2x80x9d).
For example, at the beginning of a fax call, the network has no way of knowing whether it is a fax call or a regular voice call. In general, the network allocates 64 Kbps for the call at call set-up time (i.e., no compression of the call). In the first few seconds, the input from the caller is transported un-compressed at 64 Kbps. In the ingress ATM switch, the signal is analyzed to determine whether it is a fax call or not by detecting the presence or absence of a 2100 Hz tone from the call receiving device as specified in the ITU T.30 standard.
If the gateway ATM switch decides that the call is a regular voice call, it should begin to compress the incoming signal. The gateway ATM switch should then inform the network to allocate a lower bandwidth to support this call. Conversely, the user may want to talk on the phone and subsequently transmit a fax. In this case, the bandwidth needs to be increased.
One known way to change the bandwidth of a call is through the use of the Modify command. The Modify command is an ITU standard command that allows a switch to change the traffic characteristics of an ATM connection. However, there are problems with relying on the Modify command. For one, the Modify command is not an ATM Forum standard command. Most ATM switches adhere to the ATM Forum standards. Therefore, most ATM switch vendors have not incorporated the Modify command into their switches. For a call that spans multiple networks, it is likely that the Modify command capability is not available across all ATM switches that service a call. If any switch servicing the call does not support the Modify command, the bandwidth cannot be changed using the Modify command and some bandwidth may be wasted.
Based on the foregoing, there is a need for a method and apparatus for increasing or decreasing the bandwidth of a connection over an ATM network without using the Modify command.
One embodiment of the present invention is a method of changing the characteristics of telephone call data on an ATM network that is initially transmitted via a first SVC between a first ATM switch and a second ATM switch. The method includes the steps of sending a set-up message for a second SVC from the first ATM switch to the second ATM switch and sending a switch-over request message from the first ATM switch to the second ATM switch via the second SVC. The method further includes the steps of sending a switch-over acknowledge message from the second ATM switch to the first ATM switch via the second SVC and sending a switch-over begin message from the first ATM switch to the second ATM switch via the second SVC. The method further includes the steps of sending a switch-over confirm message from the second ATM switch to the first ATM switch via the second SVC and transmitting the telephone call data via the second SVC. The steps executed by the present invention insure that the switch-over from the first SVC to the second SVC is accomplished without interrupting service.